• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1981-1986
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• 2004

A cross-flow fan relatively makes high dynamic pressure at low speed because a working fluid passes through an impeller blade twice and blades have a forward curved shape. Therefore, the performance of a cross-flow fan is influenced 25% by the impeller, 60% by the rearguider and the stabilizer, 15% by the heat exchanger. At the low flow rate, there exists a rapid pressure head reduction, a noise increase and an unsteady flow against a stabilizer and a rearguider. Moreover, it is difficult to analyze the reciprocal relations of the cross-flow fan because each parameter is independent. Numerical analyses are conducted with different starting angles of the rearguider. Two-dimensional, unsteady governing equations are solved, using FVM, PISO algorithm, sliding grid system and ${\kappa}-{\varepsilon}$ standard turbulence model.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제18권3호
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• pp.257-268
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• 2014

The objective of the present study is to investigate thermal diffusion and radiation effects on unsteady MHD flow past a linearly accelerated vertical porous plate with variable temperature and also with variable mass diffusion in presence of heat source or sink under the influence of applied transverse magnetic field. The fluid considered here is a gray, absorbing/emitting radiation but a non-scattering medium. At time t > 0, the plate is linearly accelerated with a velocity $u=u_0t$ in its own plane. And at the same time, plate temperature and concentration levels near the plate raised linearly with time t. The dimensionless governing equations involved in the present analysis are solved using the closed analytical method. The velocity, temperature, concentration, skin-friction, the rate or heat transfer and the rate of mass transfer are studied through graphs in terms of different physical parameters like magnetic field parameter (M), radiation parameter (R), Schmidt parameter (Sc), Soret number (So), Heat source parameter (S), Prandtl number (Pr), thermal Grashof number (Gr), mass Grashof number (Gm) and time (t).

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2003년도 추계 학술발표회 논문집
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• pp.299-304
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• 2003

Heat regenerator occupied by regenerative materials improves thermal efficiency of regenerative combustion system through the recovery of sensible heat of exhaust gases. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of regenerators with spherical particles were numerically analyzed to evaluate performance of ratio of waste heat recovery and temperature efficiency and to suggest optimized conditions of heat regenerator. It is predicted that exhaust gases temperature at regenerator outlet of 3.5$\times$10$^{6}$ kcal/hr heat regenerator is even lower than design condition and ratio of waste heat recovery is 75.8％.

• Journal of Advanced Marine Engineering and Technology
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• 제30권5호
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• pp.597-607
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• 2006

This paper presents a numerical simulation of the behavior of the LiBr solution droplets and falling films in horizontal tube banks of absorber. The model developed here accounts for the details of the droplets formation and impact process for absorption on horizontal tubes including the heat transfer from solution film to the tube wall. Especially. the characteristic of unsteady behavior of solution flow has been investigated. Flow visualization studies shown that the solution droplets and falling films have some of the complex characteristics. It is found that. with the numerical conditions similar to the operating condition of an actual absorption chiller/heater, the outlet solution temperature and heat flux from solution film to the tube wall have a stable periodic behavior with time. The solution droplets and falling films in horizontal tube banks of absorber is a periodic unsteady flow. The results from this model are compared with previous experimental observation taken with a high-speed digital video camera and shown good agreement.

• Journal of Computational Design and Engineering
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• 제3권4호
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• pp.349-362
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• 2016

The numerical solutions of unsteady hydromagnetic natural convection Couette flow of a viscous, incompressible and electrically conducting fluid between the two vertical parallel plates in the presence of thermal radiation, thermal diffusion and diffusion thermo are obtained here. The fundamental dimensionless governing coupled linear partial differential equations for impulsive movement and uniformly accelerated movement of the plate were solved by an efficient Finite Element Method. Computations were performed for a wide range of the governing flow parameters, viz., Thermal diffusion (Soret) and Diffusion thermo (Dufour) parameters, Magnetic field parameter, Prandtl number, Thermal radiation and Schmidt number. The effects of these flow parameters on the velocity (u), temperature (${\theta}$) and Concentration (${\phi}$) are shown graphically. Also the effects of these pertinent parameters on the skin-friction, the rate of heat and mass transfer are obtained and discussed numerically through tabular forms. These are in good agreement with earlier reported studies. Analysis indicates that the fluid velocity is an increasing function of Grashof numbers for heat and mass transfer, Soret and Dufour numbers whereas the Magnetic parameter, Thermal radiation parameter, Prandtl number and Schmidt number lead to reduction of the velocity profiles. Also, it is noticed that the rate of heat transfer coefficient and temperature profiles increase with decrease in the thermal radiation parameter and Prandtl number, whereas the reverse effect is observed with increase of Dufour number. Further, the concentration profiles increase with increase in the Soret number whereas reverse effect is seen by increasing the values of the Schmidt number.

• Journal of Mechanical Science and Technology
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• 제18권3호
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• pp.407-418
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• 2004

Prandtl-Meyer expansion flow with homogeneous condensation is investigated experimentally and by numerical computations. The steady and unsteady periodic behaviors of the diabatic shock wave due to the latent heat released by condensation are considered with a view of technical application to the condensing flow through steam turbine blade passages. A passive control method using a porous wall and cavity underneath is applied to control the diabatic shock wave. Two-dimensional, compressible Navier-Stokes with the nucleation rate equation are numerically solved using a third-order TVD (Total Variation Diminishing) finite difference scheme. The computational results reproduce the measured static pressure distributions in passive and no passive Prandtl-Meyer expansion flows with condensation. From both the experimental and computational results, it is found that the magnitude of steady diabatic shock wave can be considerably reduced by the present passive control method. For no passive control, it is found that the diabatic shock wave due to the heat released by condensation oscillates periodically with a frequency of 2.40㎑. This unsteady periodic motion of the diabatic shock wave can be completely suppressed using the present passive control method.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2003년도 춘계 학술발표회 논문집
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• pp.359-364
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• 2003

Heat regenerator occupied by regenerative materials improves thermal efficiency of regenerative combustion system through the recovery of sensible heat of exhaust gases. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of regenerator with spherical particles, were numerically analyzed to evaluate the heat transfer and pressure losses and to suggest the parameter for designing heat regenerator. It is confirmed that the computational results, such as air preheat temperature, exhausted gases outlet temperature, and pressure losses, agreed well with the experimental data conducted from Chugairo. The thermal flow in heat regenerator varies with porosity, configuration of regenerator and diameter of regenerative particle. Assuming a given exhaust gases temperature at the regenerator outlet, the regenerator length need to be linearly increased with inlet Reynolds number of exhaust gases. It is considered that inlet Reynolds number of exhaust gases should be introduced as a regenerator design parameter.

• 한국안전학회지
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• 제22권2호
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• pp.1-7
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• 2007

A problem of a unsteady time-dependent flow in a channel is of practical importance and widely considered in the design of devices such as heat exchangers, duct, and electronic equipments. The characteristics of fluid flow in channel with oscillating vortex generator was investigated experimentally. The main object of this study was to investigate the effect of the excited frequency, the excited amplitude, and Reynolds numbers on the generated frequency. Flow patterns were visualized using smoke generator and generated frequencies were measured using hot wire anemometer. When the excited frequency is increased, excited amplitude decreased and Reynolds number increased, the strength of PSD of generated frequency is decreased.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.700-710
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• 2008

A Bubble size distribution model has been developed for the numerical simulation of cryogenic high-speed cavitating flow of the turbo-pumps in the liquid fuel rocket engine. The new model is based on the previous one proposed by the authors, in which the bubble number density was solved as a function of bubble size at each grid point of the calculation domain by means of Eulerian framework with respect to the bubble size coordinate. In the previous model, the growth/decay of bubbles due to pressure difference between bubble and liquid was solved exactly based on Rayleigh-Plesset equation. However, the unsteady heat transfer between liquid and bubble, which controls the evaporation/condensation rate, was approximated by a theoretical solution of unsteady heat conduction under a constant temperature difference. In the present study, the unsteady temperature field in the liquid around a bubble is also solved exactly in order to establish an accurate and efficient numerical simulation code for cavitating flows. The growth/decay of a single bubble and growth of bubbles with nucleation were successfully simulated by the proposed model.

• 한국산학기술학회논문지
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• 제15권5호
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• pp.2628-2634
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• 2014

동절기에 차량 전면유리의 결빙이나 이물질을 제거하기 위하여 워셔액 가열시스템 적용이 점차 늘어나고 있다. 이 워셔액 가열 시스템은 짧은 시간동안 목표온도까지 워셔액이 가열되도록 설계되어야 한다. 본 연구에서는 급속하게 워셔액을 가열하기 위하여 차량 워셔액 가열 시스템의 내부 부품의 재질에 따라 열전달 특성을 해석하였다. 해석을 위해 열유동 전산해석에서 사용하고 있는 CFD(Computational Fluid Dynamics) 상용코드인 ANSYS-FLUENT 소프트웨어를 이용하였다. 본 모델은 3차원 비정상상태의 축대칭 모델로 Fluent에서 제공하는 압력기반(Pressure-Based) 기법 중의 하나인 Coupled 기법을 적용하였다. 이 결과를 통하여 충전재 및 유로의 최적화된 재질을 찾게 되었다. 충전재 재질은 낮은 밀도를 가진 공기가 실리콘카바이드보다 빠르게 가열되었다. 유로재질은 니켈보다 열전달계수가 약 4배 정도 큰 구리가 내부에 열을 균일하게 전달되어 메탄올의 가열 시간을 단축하여 효율이 더 높게 나왔다.